1. Field of the Invention
This invention relates to an electrophotographic element for use in a laser printer.
2. Description of the Related Art
Various types of electrophotographic elements have been developed, each having a photosensitive layer comprised of amorphous silicon deposited on a support member. An electrophotographic element having such an amorphous silicon photosensitive layer has many advantages, including high mechanical strength, color versatility, and long wavelength sensitivity. Developments in this type of electrophotographic element have been aimed at improving the electrophotographic characteristics of these elements. One proposal has considered the use of a photosensitive layer consisting of two sub-layers, a charge generating sub-layer and a charge transfer sub-layer. Another proposal includes providing an additional surface layer, comprised of amorphous silicon nitride.
Electrophotographic elements of the type discussed above are essential components in laser printer devices. However, prior art electrophotographic elements have caused interference fringes in laser printed copies. The printer's light source, a semiconductor laser, emits laser beams with wavelengths in the 780 to 830 nm range. When the laser printer is operated for printing, a laser beam reflected from the photographic element surface layer is superimposed on a beam reflected from the interior of the photosensitive layer or from the substrate, so that the two reflected beams interfere with each other. These reflected beams are alternately enforced and attenuated depending upon the thickness change of photosensitive layer, so that the amount of absorption in the photosensitive layer changes. The absorption change results in a potential change to the surface of the photosensitive layer. The potential change ultimately results in interference fringes in the copied image.
Various proposals have been made to address the interface problem associated with laser beam light. KOKAI Nos. 58-171038 and 61-29851 disclose proposals which attempt to reduce the reflection of beams from the substrate. KOKAI No. 61-29851 proposes a technique to reduce the reflection of beams from the surface layer. KOKAI No. 58-171038 proposes a light absorption layer containing germanium (Ge), which is formed on the substrate of the electrophotographic element. The absorption layer is provided to reduce the reflection of beams from the substrate. KOKAI No. 58-162975 uses a substrate with a coarsened surface in order to scatter the laser beams applied thereto. The technique disclosed in KOKAI No. 61-29851 employs a surface layer which has no reflection peak in the range of the wavelength of the light source .+-.50 nm. None of the above references however, have adequately solved the stated problem of interference fringes.